1. Field of the Invention
Embodiments of the invention relate to control devices for controlling the drive of a voltage-controlled switching element, such as, for example, an IGBT (Insulated Gate Bipolar Transistor).
2. Description of the Related Art
A gate drive circuit that controls the ON and OFF of an IGBT (see. e.g., Japanese Patent Application Publication No. 2009-55696) has been known in the art. This conventional device has first to third MOS transistors for turning the IGBT ON/OFF.
When turning the IGBT ON, only the first MOS transistor is turned ON to apply a power supply voltage to a gate of the IGBT. When turning the IGBT OFF, the first MOS transistor is turned OFF, and the second and third MOS transistors are turned ON, so that the charge accumulated between the gate and emitter of the IGBT is drawn out quickly during the initial stage of turning the IGBT OFF.
There is another type of conventional device. This conventional device not only controls the ON and OFF of an IGBT but also detects a current flowing to the IGBT and protects the IGBT by turning the IGBT OFF upon detection of an overcurrent.
This conventional device has a transistor for turning the IGBT ON, a transistor for turning the IGBT OFF, a transistor for protecting the IGBT from overcurrent, and various other transistors with different functions.
The transistors for turning the IGBT ON and OFF turn the IGBT ON and OFF with PWM signals and therefore require large output currents. For instance, when the rated current of the IGBT exceeds 300 A, the output currents of the transistors for turning the IGBT ON and OFF might exceed 2 A. Furthermore, the transistors for turning the IGBT ON and OFF might require a withstand voltage of 20 V or higher in order to control the drive of the IGBT.
As described above, a switching element (power device), such as an IGBT, has a rated current of several amperes to several hundred amperes, and the greater the rated current, the larger the element area of the power device. Having a large element area of the power device requires a control transistor (an output-stage transistor) of the control device controlling the drive of the power device to produce a high drive capability, which might require an output current of several amperes or more.
Due to the recent increasing demand for a high rated current of a power device, an output current of a control circuit has been increasing accordingly. However, the upper limit of a measurement current of an IC tester, which is for testing an output current of a control device, is slow to respond to such a demand prior to shipping. Thus, the upper limit has been approximately 2 A.
The design of the evaluation board can be improved by attaching a large current measuring resistor thereto, in order to measure a current greater than the upper limit by using the IC tester, but the problem is that the use of the large current measuring resistor lowers the measurement accuracy of the tester.
The use of the evaluation board with the large current measuring resistor creates a significant reduction in the measurement accuracy when the output current of the control device is low. An evaluation board with the large current measuring resistor may be used along with an evaluation board without the large current measuring resistor. A problem in this case, however, is that the costs for the testing increase due to use of the two evaluation boars. Thus, several problems exist in the related art.